In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower delays and so on (see non-patent literature 1). The specifications of LTE-advanced have been drafted for the purpose of achieving further broadbandization and higher speeds beyond LTE, and, in addition, for example, a successor system of LTE—referred to as “FRA” (Future Radio Access)—is under study.
In LTE of Rel. 8 to 12, the specifications have been drafted assuming exclusive operations in frequency bands that are licensed to operators—that is, licensed bands. For licensed bands, for example, 800 MHz, 2 GHz and/or 1.7 GHz have been in use.
LTE of Rel. 13 and later versions targets also on operations in frequency bands where license is not required—that is, unlicensed bands. For unlicensed bands, for example, 2.4 GHz, which is the same as in Wi-Fi, or the 5 GHz band and/or the like may be used. Although carrier aggregation between licensed bands and unlicensed bands (LAA: license-assisted access) is under study in Rel. 13 LTE, there is a possibility that, in the future, dual connectivity and unlicensed-band stand-alone may be studied as well.
In unlicensed bands, interference control functionality is likely to be necessary in order to allow co-presence with other operators' LTE, Wi-Fi, or different systems. In Wi-Fi, the function called “LBT” (Listen Before Talk) or “CCA” (Clear Channel Assessment) is implemented as an interference control function. In Japan and Europe, the LBT function is stipulated as mandatory in systems that are run in the 5 GHz unlicensed band, such as Wi-Fi.